docs: def populate(self):
          """Populates a new cache.
  
          """
          if self.exists:
              raise CacheAlreadyExistsException('location: %s' % self.cache_uri)
  
          self._populate_setup()
  
          with closing(self.graph):
              with self._download_metadata_archive() as metadata_archive:
                  for fact in self._iter_metadata_triples(metadata_archive):
                      self._add_to_graph(fact)